Conventionally, in refrigeration cycle apparatuses such as heat pump apparatuses, fin-tube type heat exchangers are often used. A fin-tube type heat exchanger has a configuration in which a heat transfer tube through which refrigerant flows is provided with a heat transfer fin to increase the heat transfer area.
FIG. 11 illustrates a configuration of conventional fin-tube type heat exchanger 100 disclosed in PTL 1. Heat exchanger 100 includes a plurality of stacked heat transfer fins 120 and heat transfer tube 110 that penetrates heat transfer fins 120.
Heat transfer fin 120 includes tubular collar part 123 (having a constant cross-sectional shape) that is provided in an upright state with respect to plate-shaped base part 121. From the root and an end of collar part 123, root part 122 and flare part 124 are expanded outward in the radial direction of collar part 123 while being curved.
The pitch of heat transfer fins 120 (interval between base parts 121) is defined when flare part 124 of one of two adjacent heat transfer fins 120 makes contact with base part 121 located near root part 122 of the other of heat transfer fins 120.
Normally, expansion of heat transfer tube 110 is performed in order to bring each heat transfer tube 110 into close contact with each heat transfer fin 120. To be more specific, heat transfer tube 110 having an outer diameter smaller than the inner diameter of collar part 123 is inserted in collar part 123 of stacked heat transfer fins 120. Thereafter, heat transfer tube 110 is expanded and thus heat transfer tube 110 and each heat transfer fin 120 are closely bonded together.
At the time of the expansion, heat transfer tube 110 contracts in the tube-axial direction. To prevent deformation of heat transfer fin 120 at this time, step part 125 is provided to increase the strength of heat transfer fin 120 in heat transfer fin 120 disclosed in PTL 1.
In heat transfer fin 120, root part 122 and flare part 124 are expanded while being curved, and therefore relatively large gap 130 is formed between collar parts 123 of heat transfer fins 120 adjacent each other.
When such a gap 130 is interposed, the contact area between heat transfer tube 110 and collar part 123 is small, and heat is not easily transmitted from heat transfer tube 110 to heat transfer fin 120. To solve such a problem, in PTL 2, gap 130 is filled with filler such as silicone resin to improve thermal conductivity.